pablocruise

The copper is showing (red circles) in places I didn't expect. I thought it was only to show near the centers? These have approx 20K-30K miles on them. That's how long ago motor was rebuilt by a shop locally. The rear and fronts seem ok, but the centers don't seem to have correct wear pattern. Maybe this has something to do with the #7 piston wrist pin bore breaking? Crank mains look fine.
Whaddaya guys think about the wear patterns for so little miles?





[Modified by 89 Paul in Cal, 4:22 AM 4/22/2003]

jimswhite92

Lots of good links here

http://forums.corvetteforum.com/zerothread?id=542486

grumpyvette

look very carefully at the pictures below


http://www.thirskauto.net/BearingPics.html


here this will help http://www.babcox.com/editorial/us/uhs89734.htm

http://www.thirskauto.net/BearingPics.html


http://www.kcenginepro.com/install.htm


http://www.bobistheoilguy.com/bearin...aranalysis.htm


http://www.aera.org/tech/tb1465r.htm


http://www.hadmac.com/technical_info.htm

http://www.babcox.com/editorial/ar/ar20128.htm

http://www.babcox.com/editorial/cm/cm99828.htm

http://www.thirskauto.net/Engine_Thrust_Bearings.html

http://www.aera.org/tech/tb1465r.htm

http://www.dragnbreath.com/Clevite/TN%2016.html

http://www.dragnbreath.com/Clevite/TN%2022.html

http://www.dragnbreath.com/Clevite/TN%2028cambrgs.html


http://www.diabolicalperformance.com/clearances.html

http://www.jimcookperformance.com/Te...28cambrgs.html

http://www.babcox.com/editorial/ar/ar10180.htm

http://www.babcox.com/editorial/us/uhs69720.htm

http://www.automotiveengine.com/../eng_inst.htm


personally looking at the un-even wear pattern Id say either the block or crank is slightly warped or the main caps on the block were not torqued down to the correct preload in stages correctly, Id have the block checked and line honed if it needs it and the crank looked at by a good shop IF you intend to keep it, (if its a cast crank Id dumpster it and get a forged, internally ballanced rotateing assembly WITH A GOOD FLUIDAMPER and with FORGED pistons and free floating piston pins like Ive been useing.BTW that connecting rod on that broken piston may be slightly warped due to the un-even loads it indured, CHECK IT CAREFULLY or just replace it, your lucky you pulled the engine down BEFORE that rod came loose!! at least now the block, heads,rods,and crank may be salvageable. but ID install a fully forged rotateing assembly with a max stroke and a reasonably high static compression ratio to get my DYNAMIC COMPRESSION RATIO at about 8.2:1 with the cam of my choice
http://www.scatcrankshafts.com/catalog02.html
http://www.crower.com/

http://www.holley.com/HiOctn/ProdLin...KA/IECEKA.html
http://www.flatlanderracing.com/index.html (stroker kits, chevy,sbc)





[Modified by grumpyvette, 3:54 PM 4/22/2003]

Phobos84

Mine looked worse then yours with less miles on it. Mine was caused by a non oiled K&N filter. There was all kinds of dirt and grit in my engine and it cut the bearings up, bad. On mine it was all copper showing and they all had deep gashes in them.

ittlfly

It looks like the block needs to be line bored for trueness. Also. the crank probably needs to be turned. The wear shows that the crank doesn't have sufficient clearance at the main caps during rotation. Was it machined at the last rebuild? Who checked the clearances at the time? You might try another machine shop this time? BTW, verify all the clearances yourself. :D

VetNutJim

Your bearing wear isn't PERFECT but that had NOTHING to do with your piston failure.
My belief is you just caught a unlucky break (pun intended) on the piston that failed.
Put it back together with some good Clevite77 TRi-Metal bearings and let it rip.
That bearing wear is FINE for a street engine.

If you have the resource, have the other pistons magnafluxed for cracks in the pin web area. It'll give you peace of mind, anyway since ONE already broke.
Might as well have the rods & crank magnafluxed if it'll make you feel beter.
Your engine will be fine.. just CAREFULLY put it back together.
Measure ALL the bearing clearances with plastigage if you don't have the micrometers.

Good luck with it.

Just thought of this:

That piston "may" have been damaged when the pin was pressed in.
That would be one reason it could have failed.
The pin clearance may have been too tight on that one, also.

Over and out...


[Modified by VetNutJim, 1:19 PM 4/22/2003]

weekendwrench

I would also suggest that you need to have the block align bored and the crank turned or at least polished. I am wondering if the block was assembled with the main caps not in the original locations.

CorvetteZ51Racer

Ok, got a short list for ya:

1) pistons (or anything aluminum for that matter) can't be magnafluxed. There are ways to check for cracks, but I personally wouldn't bother because of some items to follow.

2) More than likely your bearing wear is due to one of three things: either the main journals aren't true, the caps are installed in the wrong order or wrong orientation, or your crank has some cracks in it and it's not completely staight. Any of those things could cause your problems.

What I would do:
1) completely tear down the motor and take the block to a machine shop. Have them check the crank for cracks and straightness. Have them check the rods for straightness and to resize them. On the block, have it checked for any scoring or anything that would require an overbore or significant hone (0.010" cuts are typically done with a hone). Have them alignhone the mains. I would personally throw away every single one of those pistons and replace them. If you go back with press fit pins (which you should if you're sticking with the stock rods) make sure whoever is press fitting the new pistons to the rods does a pin fit before doing the installation. Failing to pin fit can cause the pin land to break like that.

When you reassemble the motor, make sure all of the bearing clearances are correct. If you have a micrometer and dial bore gauge, that's best, but plastigauge will do. When you have the crank installed, make sure that you can "throw" the crank around AT LEAST one full revolution before it stops. If it doesn't, something's too tight and needs to be clearanced. I spent 2-3 hours doing the thrust bearing on my most recent rebuild, because as the bearing was cast I had less than 0.001" clearance, and you need between 4 and 7 thousandths on a SBC. Just an example. Take your time making sure all of the clearances are right and making sure that everything spins and moves as it should, and you won't get that bearing wear.

pablocruise

Awesome information guys!
I will take the shortbolck to a better shop and have them check everything. I hope I can at least save the block. I'd love to buy a 400 crank/rods/FORGED pistons. At least I can sell that easily. If, not.....
boat anchors for sale cheap!

r15752

Your bearings look fine to me with 20 30 k on them. I would say the second from the right the wear is from getting less oil then the others. how hard are you on it .did you have the crank turned? hope this helps . :chevy :auto:

CorvetteZ51Racer

If the wear was centered on the bottom of the bearing and in the middle, it would be fine. It's the fact that the wear is higher up the bearing and on the edges, diagonally across the center of the journal that is the source of concern.

MyZ51

Looks like at least a align hone or bore is in order. I also agree about a mis installed piston pin causing this type of failure. You're really lucky you got it apart before it turned to a grenade.

AquaMetallic94LT1

You might have had a detonation problem, bad harmonic balancer (but the front bearing would be chewed up by that one) or balance problem. It looks like there was enough pressure on the rotating assy to cause some contact between the crankshaft and the bearing surfaces. Notice how they coincide with the cylinder bores. I'd like to know how the rod bearing surfaces look.

VetNutJim

Re: Magnaflux

CorvetteZ51 Racer is correct about non-ferrous metal magnaflux.
However you CAN magnaflux the crank and rods. ZyGlo the pistons.

I believe you said the engine had run for 30,000 miles?
If it ran that long, you don't have a bearing problem that needs any attention.

Most of the bearing wear occurs during cranking...before the oil is pumped into the journal under pressure.
There is normally some oil left in the bearing clearance space to provide a little hydrodynamic lubrication but often not enough to TOTALLY eliminate a little crank to bearing scrub.

The bearing material is so soft you can scratch it with your fingernail.
THis is so any particle that happens to end up in the journal space will sink into the bearing and not sit and scroll a scratch in the crank.

Don't concern yourself with the main bearings. Put some good quality new ones back in there, check the clearances and forget about'em.

Replace the piston/pin that broke and you should be back in the race.